Optical distance measurement system and method

ABSTRACT

There is provided an optical distance measurement system including an image sensor and a processing unit. The processing unit is configured to generate an image to be calculated according to at least one image captured by the image sensor, wherein different image regions of the image to be calculated correspond to different exposure times thereby improving the accuracy of the distance calculation.

RELATED APPLICATIONS

The present application is based on and claims priority to TaiwaneseApplication Number 103138317, filed Nov. 4, 2014, the disclosures ofwhich are hereby incorporated by reference herein in their entirety.

BACKGROUND

1. Field of the Disclosure

This disclosure generally relates to a distance measurement system and,more particularly, to an optical distance measurement system and methodutilizing multiplexing exposure mechanism.

2. Description of the Related Art

An optical distance measurement system may calculate an object distanceusing a triangulation method. For example, the optical distancemeasurement system includes a light source and a camera. The lightsource projects light to an object to be detected, and the camerareceives reflected light from the object to be detected to generate animage frame. When a spatial relationship between the light source andthe camera is already known, a distance of the object to be detected isobtainable using the triangulation method according to an object imageposition in the image frame.

However, when a plurality of objects at different distances is presentin the space at the same time, an object at a near distance could causeover exposure whereas an object at a far distance could cause underexposure such that the calculation accuracy of the optical distancemeasurement system is degraded. Especially, when the object at a fardistance is under exposure, it may not be able to calculate the objectdistance of the object at a far distance.

SUMMARY

Accordingly, the present disclosure further provides an optical distancemeasurement system and method that reserve information of both far andnear objects in the image frame so as to improve the calculationaccuracy.

The present disclosure provides an optical distance measurement systemand method that utilize time-multiplexed exposure mechanism.

The present disclosure provides an optical distance measurement systemand method that utilize spatial-multiplexed exposure mechanism.

The present disclosure provides an optical distance measurement systemincluding an image sensor and a processing unit. The image sensor isconfigured to capture a first image with a first exposure time andcapture a second image with a second exposure time, wherein the firstexposure time is different from the second exposure time. The processingunit is configured to receive the first image and the second image,divide the first image into a plurality of first image regions, dividethe second image into a plurality of second image regions, comparesignal features of the first image regions and the second image regionsat corresponding regions, and combine the first image region having alarger signal feature than the corresponding second image region withthe second image region having a larger signal feature than thecorresponding first image region to form a combined image.

The present disclosure further provides an optical distance measurementsystem including an image sensor and a processing unit. The image sensoris configured to capture a reference image with a reference exposuretime and capture different image regions of a current image with aplurality of exposure times. The processing unit is configured toreceive the reference image, divide the reference image into a pluralityof image regions, respectively calculate an average brightness value ofeach of the plurality of image regions of the reference image, andcontrol the plurality of exposure times of the image sensor forcapturing the different image regions of the current image.

The present disclosure further provides a distance measurement method ofan optical distance measurement system including the steps of:capturing, by an image sensor, a first image with a first exposure time;capturing, by the image sensor, a second image with a second exposuretime; dividing the first image into a plurality of first image regionsand calculating a first signal feature of each of the first imageregions; dividing the second image into a plurality of second imageregions and calculating a second signal feature of each of the secondimage regions; comparing the first signal feature of each of the firstimage regions with the second signal feature of the corresponding secondimage region; and combining the first image region having the firstsignal feature larger than the corresponding second signal feature withthe second image region having the second image feature larger than thecorresponding first signal feature to form a combined image.

The present disclosure further provides a distance measurement method ofan optical distance measurement system including the steps of:capturing, by an image sensor, a reference image with a referenceexposure time; dividing the reference image into a plurality of imageregions and calculating an average brightness value of each of theplurality of image regions; and respectively capturing, by the imagesensor, different image regions of a current image with a plurality ofexposure times according to the average brightness values.

The present disclosure further provides an optical distance measurementsystem including an image sensor and a processing unit. The image sensoris configured to capture a first image and a second image respectivelywith different exposure times. The processing unit is configured toreceive the first image and the second image, and combine a part ofimage regions of the first image and a part of image regions of thesecond image to form a combined image.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 is a schematic block diagram of an optical distance measurementsystem according to one embodiment of the present disclosure.

FIG. 2 is a schematic diagram of an optical distance measurement systemaccording to one embodiment of the present disclosure.

FIG. 3 is a flow chart of a distance measurement method of an opticaldistance measurement system according to a first embodiment of thepresent disclosure.

FIG. 4A is a timing diagram of the image capturing of an opticaldistance measurement system according to the first embodiment of thepresent disclosure.

FIG. 4B is an operational schematic diagram of an optical distancemeasurement system according to the first embodiment of the presentdisclosure.

FIG. 5 is a flow chart of a distance measurement method of an opticaldistance measurement system according to a second embodiment of thepresent disclosure.

FIG. 6A is a timing diagram of the image capturing of an opticaldistance measurement system according to the second embodiment of thepresent disclosure.

FIG. 6B is an operational schematic diagram of an optical distancemeasurement system according to the second embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Referring to FIG. 1, it is a schematic block diagram of an opticaldistance measurement system according to one embodiment of the presentdisclosure. The optical distance measurement system 1 includes an imagesensor 11 and a processing unit 13. The image sensor 11 is preferably anactive image sensor, e.g. a CMOS image sensor, which may change anexposure time for capturing an image F or respectively capture differentimage regions of the image F with a plurality of exposure times(illustrated below).

The processing unit 13 is, for example, a digital signal processor(DSP), a microcontroller (MCU) or a central processing unit (CPU), andconfigured to receive images F outputted by the image sensor 11 toperform the post-processing and to control the image capturing of theimage sensor 11. In one embodiment, the processing unit 13 includes anexposure control unit 131, a multiplexing module 133 and a distancecalculation unit 135, wherein the exposure control unit 131, themultiplexing module 133 and the distance calculation unit 135 are dataprocessors in the processing unit 13 and may be implemented by softwareor hardware without particular limitations. It is appreciated thatalthough FIG. 1 shows that the processing unit 13 includes differentoperation modules for illustration purpose, it can be said that thefunctions executed by these operation modules in the processing unit 13are executed by the processing unit 13.

The exposure control unit 131 is configured to control the image sensor11 to capture all image regions of different images F with differentexposure times (i.e. one image corresponding to one exposure time), orto capture different image regions of a same image F with a plurality ofexposure times (i.e. one image corresponding to a plurality of exposuretimes). The multiplexing module 133 is configured to process the imagesF received by the processing unit 13 in a time multiplexed manner or aspatially multiplexed manner, and generate an image to be calculated Fm(e.g. the combined image or current image mentioned below). The distancecalculation unit 135 is configured to calculate at least one objectdistance according to the image to be calculated Fm using apredetermined algorithm, e.g. calculating the object distance using thetriangulation method.

Referring to FIG. 2, it is a schematic diagram of an optical distancemeasurement system according to one embodiment of the presentdisclosure. The optical distance measurement system 1 may furtherinclude a light source 15 configured to project a two-dimensional lightsection (e.g. an optical line with a predetermined width) onto an object9, wherein the light source 15 is, for example, a coherent light source,a partially coherent light source or an incoherent light source withoutparticular limitations. The light source 15 is configured to emitvisible light or invisible light. The image sensor 11 receivesreflective light from the object 9 and then generates an image Fcontaining a reflective light image 19 to be sent to the processing unit13. The processing unit 13 firstly uses the multiplexing mechanism(illustrated by examples below) of the present disclosure to generate animage to be calculated Fm according to the image F, and then calculatesat least one object distance D according to the image to be calculatedFm, wherein the image to be calculated Fm also includes a reflectivelight image 19. More specifically speaking, at least a part of aplurality of exposure times corresponding to different image regions ofthe image to be calculated Fm are different from each other (illustratedby examples below) such that the brightness of the reflective lightimage 19 in each of the image regions is suitable to calculate theobject distance D. In addition, in some embodiments the processing unit13 outputs the image to be calculated Fm in a wired or wireless mannerto an external device, e.g. an external host, to be post-processed. Itshould be mentioned that although FIG. 2 shows that the two-dimensionallight section projected by the light source 15 is not a continuoussection, but it is only intended to illustrate but not to limit thepresent disclosure.

In one embodiment, the processing unit 13 may include a storage unit(not shown) for storing a look-up table, which includes the relationshipof positions of the reflective light image 19 versus object distances D.Accordingly, after the processing unit 13 obtains the position of thereflective light image 19 in the image to be calculated Fm, at least oneobject distance D is obtainable directly according to the look-up table,wherein the look-up table is calculated according to a spatialrelationship (e.g. a distance L) between the light source 15 and theimage sensor 11 and according to a projection angle of the light source15, and the look-up table is previously stored in the storage unit. Inanother embodiment, the storage unit of the processing unit 13 stores adistance calculation algorithm, and after the position of the reflectivelight image 19 in the image to be calculated Fm is obtained, at leastone object distance D is calculated according to the distancecalculation algorithm.

In the embodiments of the present disclosure, as the light source 15 isconfigured to project a two-dimensional light section, the image Foutputted by the image sensor 11 contains a linear reflective lightimage 19. The processing unit 13 is able to calculate a plurality ofobject distances at the same time (e.g. different objects correspondingto different parts of the reflective light image and at differentpositions) to have a better adaptability. Finally, the processing unit13 outputs, e.g. to a host or a computer system, the calculated objectdistance D to perform corresponding controls, wherein the controllablefunction corresponding to the object distance D is determined accordingto different applications.

Referring to FIG. 3, it is a flow chart of a distance measurement methodof an optical distance measurement system according to a firstembodiment of the present disclosure, which includes the steps of:capturing a first image with a first exposure time (Step S31); capturinga second image with a second exposure time (Step S32); dividing thefirst image into a plurality of first image regions and calculating afirst signal feature of each of the first image regions (Step S33);dividing the second image into a plurality of second image regions andcalculating a second signal feature of each of the second image regions(Step S34); comparing the first signal features with the second signalfeatures (Step S35); and combining the first image region having thefirst signal feature larger than the corresponding second signal featurewith the second image region having the second image feature larger thanthe corresponding first signal feature to form a combined image (StepS36).

Referring to FIGS. 1-3 and 4A-4B together, details of the firstembodiment are illustrated hereinafter. The processing unit 13 controlsthe light source 15 to activate when the image sensor 11 is capturing animage F such that the image F captured by the image sensor 11 contains areflective light image 19 from the object 9 to accordingly calculate anobject image D of the object 9.

Step S31: The image sensor 11 is controlled by the exposure control unit131 of the processing unit 13 to capture a first image F_(S) with afirst exposure time ET_(S).

Step S32: Then, the image sensor 11 is controlled by the processing unit13 to capture a second image F_(L) with a second exposure time ET_(L),wherein the first image F_(S) and the second image F_(L) are two imagesF successively or separated by at least one image captured by the imagesensor 11, and the first exposure time ET_(S) is different from thesecond exposure time ET_(L). It should be mentioned that although FIG.4A shows that the first exposure time ET_(S) is smaller than the secondexposure time ET_(L), the present disclosure is not limited thereto. Insome embodiments, the first exposure time ET_(S) is larger than thesecond exposure time ET_(L). In one embodiment, the exposure controlunit 131 of the processing unit 13 controls the image sensor 11 tocapture images alternatively with the first exposure time ET_(S) and thesecond exposure time ET_(L).

Step S33: After the processing unit 13 receives the first image F_(S),the multiplexing module 133 divides, in a predetermined manner, thefirst image F_(S) into a plurality of first image regions, e.g. A1 to A4(referring to FIG. 4B), and calculates a first signal feature C1 to C4of each of the first image regions A1 to A4 (referring to FIG. 4B),wherein each of the first image regions A1 to A4 is one pixel row, aplurality of pixel rows, one pixel column, a plurality of pixel columnsor a rectangular pixel region of the first image F_(S), and is notlimited to that shown in FIG. 4B. In one embodiment, the signal featuresC1 to C4 are signal-to-noise ratios (SNR) of the first image regions A1to A4, respectively. For example, the multiplexing module 133 separatessignal data and noise data in each of the first image regions A1 to A4according to a dynamic threshold, and calculates a ratio of an energysum of all signal data and an energy sum of all noise data in each ofthe first image regions A1 to A4 to be configured as the SNR. In oneembodiment, the dynamic threshold is selected as, for example, anaverage value obtained by dividing a maximum energy of one first imageregion by a sum of average energy of all first image regions, but thepresent disclosure is not limited thereto. Accordingly, one threshold isobtained for each of the first image regions A1 to A4. As the thresholdfor each of the first image regions A1 to A4 is calculated according tothe captured image data, the thresholds may be different from each otherand thus the thresholds are referred to dynamic thresholds in thepresent disclosure.

Step S34: Similarly, after the processing unit 13 receives the secondimage F_(L), the multiplexing module 133 divides, in the predeterminedmanner (identical to the Step S33), the second image F_(L) into aplurality of second image regions, e.g. A1′ to A4′ (referring to FIG.4B), and calculates a second signal feature C1′ to C4′ of each of thesecond image regions A1′ to A4′ (referring to FIG. 4B), wherein each ofthe second image regions A1′ to A4′ is one pixel row, a plurality ofpixel rows, one pixel column, a plurality of pixel columns or arectangular pixel region of the second image F_(L), and is not limitedto that shown in FIG. 4B. Similarly, the signal features C1′ to C4′ aresignal-to-noise ratios (SNR) of the second image regions A1′ to A4′,respectively. For example, the multiplexing module 133 separates signaldata and noise data in each of the second image regions A1′ to A4′according to a dynamic threshold, and calculates a ratio of an energysum of all signal data and an energy sum of all noise data to beconfigured as the SNR. The method of determining the dynamic thresholdis similar to that of Step S33 and thus details thereof are not repeatedherein.

Step S35: Next, the multiplexing module 133 compares the first signalfeature of each of the first image regions A1 to A4 with the secondsignal feature of the corresponding second image regions A1′ to A4′. Forexample, the multiplexing module 133 compares the first signal featureC1 of the first image region A1 with the second signal feature C1′ ofthe second image region A1′; compares the first signal feature C2 of thefirst image region A2 with the second signal feature C2′ of the secondimage region A2′; compares the first signal feature C3 of the firstimage region A3 with the second signal feature C3′ of the second imageregion A3′; and compares the first signal feature C4 of the first imageregion A4 with the second signal feature C4′ of the second image regionA4′.

Step S36: Next, the multiplexing module 133 combines, in a timemultiplexed manner, a part of image regions of the first image F_(S)with a part of image regions of the second image F_(L) to form acombined image Fm. In one embodiment, the multiplexing module 133combines the first image region having the first signal feature largerthan the corresponding second signal feature with the second imageregion having the second image feature larger than the correspondingfirst signal feature to form a combined image Fm. For example, it isassumed herein that the first signal features C1 and C4 are respectivelylarger than the second signal features C1′ and C4′, and this means thatthe first image regions A1 and A4 are more suitable to calculate acorrect object distance than the second image regions A1′ and A4′.Meanwhile, it is assumed herein that the first signal features C2 and C3are respectively smaller than the second signal features C2′ and C3′,and this means that the second image regions A2′ and A3′ are moresuitable to calculate a correct object distance than the first imageregions A2 and A3. Then, the multiplexing module 133 forms a combinedimage Fm which includes image regions A1, A2′, A3′ and A4 as shown inFIG. 4B.

It is appreciated that although FIG. 4B shows that a combined image Fmrespectively includes a part of image regions of the first image F_(S)(e.g. A1 and A4) and a part of image regions of the second image F_(L)(e.g. A2′ and A3′), but the present disclosure is not limited thereto.According to the image F actually captured by the image sensor 11, thecombined image Fm may be identical to the first image F_(S) or thesecond image F_(L).

Finally, the distance calculation unit 135 of the processing unit 13calculates at least one object distance D according to the combinedimage Fm. It should be mentioned that in this embodiment a number ofsaid at least one object distance may be determined according to anumber of pixel rows of the image F. For example, one object distance isobtained corresponding to each pixel row, or one object distance isobtained corresponding to a plurality of pixel rows (e.g. 2 to 5 pixelrows) depending on the identification resolution. The distancecalculation unit 135 also identifies an object number according to theplurality of object distances being obtained, and merges the objectdistances associated with the same object to one object distance suchthat the distance calculation unit 135 finally outputs a number of theobject distances D identical to a number of the objects to be detected.

In addition, although FIGS. 4A and 4B show that the processing unit 13compares the signal features of different image regions between twoimages F and generates a combined image Fm, but the present disclosureis not limited thereto. In some embodiments, the processing unit 13 maycompare signal features of different image regions between more than twoimages F and generate a combined image. In this case, in the Step S36each image region having a maximum signal feature in corresponded imageregions of more than two images is selected to form the combined imageFm, and details in other Steps S31 to S35 are similar to the firstembodiment and thus details thereof are not repeated herein. In otherwords, the multiplexing module 133 of this embodiment may divide eachimage F captured by the image sensor 11 into identical (e.g. identicalposition and size) image regions such that the combined image Fm canhave a size identical to the image F.

In a word, in the above embodiment, the processing unit 13 combinesdifferent partial image regions of different image frames to form acombined image according to the image quality of the partial imageregions so as to calculate at least one object distance according to thecombined image, wherein shapes and sizes of the partial image regions donot have particular limitations. For example, the processing unit 13 maycombine, according to the image quality (e.g. the signal feature), apart of image regions in the first image F_(S), e.g. a part of A1 to A4,with a part of image regions in the second image F_(L), e.g. a part ofA1′ to A4′, to form a combined image Fm.

Referring to FIG. 5, it is a flow chart of a distance measurement methodof an optical distance measurement system according to a secondembodiment of the present disclosure, which includes the steps of:capturing a reference image with a reference exposure time (Step S51);dividing the reference image into a plurality of image regions andcalculating an average brightness value of each of the plurality ofimage regions (Step S52); and respectively capturing different imageregions of a current image with a plurality of exposure times accordingto the average brightness values (Step S53).

Referring to FIGS. 1-2, 5 and 6A-6B, details of the second embodiment ofthe present disclosure are described hereinafter. Similarly, theprocessing unit 13 also controls the light source 15 to emit light whenthe image sensor 11 is capturing images F.

Step S51: The image sensor 11 is controlled by the exposure control unit131 of the processing unit 13 to capture a reference image F_(T) with areference exposure time ETr. In this embodiment, the reference imageF_(T) is configured to identify a plurality of exposure times ET forcapturing a current image (e.g. F_(T+1)), and is not used to calculatean object distance D.

Step S52: After the processing unit 13 receives the reference imageF_(T), the multiplexing module 133 calculates, in a spatiallymultiplexed manner, average brightness values of a plurality of imageregions in the reference image F_(T) so as to determine a plurality ofexposure times for capturing an image to be calculated Fm. For example,the multiplexing module 133 divides the reference image F_(T) into aplurality of image regions A1 to A4 (referring to FIG. 6B), andrespectively calculates average brightness values AV1 to AV4 of theimage regions A1 to A4 (referring to FIG. 6B), wherein each of thedifferent image regions A1 to A4 is one pixel row, a plurality of pixelrows, one pixel column, a plurality of pixel columns or a rectangularpixel region of the current image F_(T+1), and is not limited to thatshown in FIG. 6B.

Step S53: Finally, the exposure control unit 131 of the processing unit13 controls the corresponding exposure times ET1 to ET4 (referring toFIGS. 6A to 6B) for capturing different image regions A1 to A4 of acurrent image F_(T+1) according to the average brightness values AV1 toAV4. In one embodiment, the multiplexing module 133 of the processingunit 13 determines the plurality of exposure times ET1 to ET4 accordingto a comparison result of comparing the average brightness values AV1 toAV4 of the image regions A1 to A4 of the reference image F_(T) with atleast one threshold. For example, when identifying that the averagebrightness value AV1 is between two thresholds of a plurality ofthresholds (or within one of a plurality of brightness intervals), themultiplexing module 133 directly determines, according to an exposuretime (previously set and stored) corresponding to the two thresholds,the exposure time for capturing the image region A1 of the current imageF_(T+1) as ET1. The exposure times ET2 to ET4 corresponding to otherimage regions A2 to A4 are determined in the same way. In thisembodiment, the current image F_(T+1) is configured as the image to becalculated Fm.

Finally, the distance calculation unit 135 of the processing unit 13calculates at least one object distance D according to the current imageF_(T+1).

In another embodiment, the multiplexing module 133 adjusts one exposuretime step every time such that not all of the exposure times ET1 to ET4corresponding to the image regions A1 to A4 of the current image F_(T+1)are adjusted to target values according to one reference image F_(T). Inthis case, when one of the brightness values of different image regionsA1 to A4 of the current image F_(T+1) is not within a predeterminedbrightness range, the exposure control unit 131 of the processing unit13 may control a plurality of exposure times of the image sensor 11 forcapturing different image regions A1′ to A4′ of a next image F_(T+2)(referring to FIG. 6A) according to the average brightness values of thedifferent image regions A1 to A4 of the current image F_(T+1). When themultiplexing module 133 of the processing unit 13 identifies that allthe brightness values of the image regions A1′ to A4′ of the next imageF_(T+2) are within a predetermined brightness range to be suitable forcalculating the object distance, the distance calculation unit 135 ofthe processing unit 13 then calculates at least one object distance Daccording to the next image F_(T+2). It is appreciated that theplurality of exposure times corresponding to the different image regionsA1′ to A4′ of the next image F_(T+2) may be partially identical to ortotally different from the plurality of exposure times corresponding tothe different image regions A1 to A4 of the current image F_(T+1)depending on the average brightness values of the different imageregions A1 to A4 of the current image F_(T+1). When one of the averagebrightness values of the different image regions A1′ to A4′ of the nextimage F_(T+2) is still not within a predetermined brightness range, theadjustment is continuously performed till average brightness values ofall the image regions A1 to A4 are within the predetermined brightnessrange.

It should be mentioned that although in the Step S51 the image sensor 11is illustrated by using one reference exposure time ETr as an example,the image sensor 11 may capture different image regions, e.g. imageregions A1 to A4 shown in FIG. 6B, of the reference image F_(T) with aplurality of identical exposure times ETr.

It should be mentioned that although in the above second embodiment thereference image F_(T) is not used to calculate the object distance D,when average brightness values AV1 to AV4 of all the image regions A1 toA4 of the reference image F_(T) are within a predetermined brightnessrange, the distance calculation unit 135 may directly calculate theobject distance D according to the reference image F_(T) withoutinforming the exposure control unit 133 via the multiplexing module 133to control the image sensor 11 to capture the current image F_(T+1) withdifferent exposure times ET, wherein the predetermined brightness rangemay be previously set and stored in a storage unit.

Similarly, a number of the at least one object distance D is determined,for example, according to a number of pixel rows of the image F and anumber of objects 9 without particular limitations.

It should be mentioned that although FIG. 6A shows that every imageregion A1 to A4 corresponds to different exposure times ET1 to ET4, butit is only intended to illustrate but not to limit the presentdisclosure. According to the image content actually being captured, onlya part of the plurality of exposure times ET1 to ET4 corresponding tothe different image regions A1 to A4 of the current image F_(T+1) aredifferent from each other.

In addition, in order to further eliminate the influence from ambientlight, the processing unit 13 further controls the light source 15 toactivate and deactivate corresponding to the image capturing of theimage sensor 11, e.g. capturing a bright image corresponding to theactivation of the light source 15 and capturing a dark imagecorresponding to the deactivation of the light source 15. The processingunit 13 further calculates a differential image between the bright imageand the dark image to be configured as the first image F_(S) and thesecond image F_(L) of the first embodiment, or configured as thereference image F_(T), the current image F_(T+1) and the next imageF_(T+2) of the second embodiment.

In the above embodiment, the multiplexing module 133 of the processingunit 13 is configured to divide the image F and calculate signalfeatures, e.g. the SNR or average brightness value, of different imageregions so as to determine whether to output an image to be calculatedFm to the distance calculation unit 135 for calculating at least oneobject distance D. In the first embodiment, the exposure control unit131 controls the image sensor 11 to capture different images (e.g. F_(S)and F_(L)) with predetermined exposure times, and thus the exposuretimes that the exposure control unit 131 controls the image sensor 11 tocapture different images F are fixed predetermined values (e.g. ET_(S)and ET_(L) in FIG. 4A). In the second embodiment, the multiplexingmodule 133 determines the exposure times corresponding to differentimage regions according to average brightness values of the differentimage regions and informs the exposure control unit 131, and thus theexposure times that the exposure control unit 131 controls the imagesensor 11 to capture the different image regions may not be fixedpredetermined values and are determined according to the actualcalculation results (e.g. average brightness values).

As mentioned above, the conventional optical distance measurement systemhas the problem of unable to accurately measure objects at differentpositions. Especially an object at a far distance may not be measured.Therefore, the present disclosure further provides an optical distancemeasurement system (FIGS. 1 and 2) and an optical distance measurementmethod (FIGS. 3 and 5) that reserve image information of objects to bedetected at different distances through time multiplexed manner orspatially multiplexed manner so as to improve the calculation accuracy.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. An optical distance measurement system,comprising: a single light source configured to project an optical lineon an object; an image sensor configured to capture reflected light fromthe optical line on the object projected by the single light source togenerate a first image with a first exposure time, and capture reflectedlight from the optical line on the object projected by the same singlelight source to generate a second image with a second exposure time,wherein the first exposure time is different from the second exposuretime; and a processing unit coupled to the image sensor, and configuredto receive the first image and the second image, divide the first imageinto a plurality of first image regions, each having multiple pixels,and calculate a signal-to-noise of each of the first image regions,divide the second image into a plurality of second image regions, eachhaving multiple pixels, corresponding to the plurality of first imageregions and calculate a signal-to-noise of each of the second imageregions, compare the signal-to-noise ratios of the first image regionsin the first image and the corresponding second image regions in thesecond image to determine which of the first image regions and secondimage regions have a larger signal-to-noise ratio, and combine the firstimage region having the larger signal-to-noise ratio than thecorresponding second image region with the second image region havingthe larger signal-to-noise ratio than the corresponding first imageregion to form a combined image that reserves information of differentobjects at different distances in images captured by the image sensor toimprove calculation accuracy, wherein the combined image has a pluralityof image regions each being either (i) a first image region selectedfrom the plurality of first image regions or (ii) a corresponding secondimage region selected from the plurality of second image regions, sothat some image regions of the plurality of image regions of thecombined image are selected from the plurality of first image regions,and remaining image regions of the plurality of image regions of thecombined image are selected from the plurality of second image regions.2. The optical distance measurement system as claimed in claim 1,wherein the first image contains a first light image associated with theoptical line and included in each of the first image regions; the secondimage contains a second light image associated with the optical line andincluded in each of the second image regions; and the combined image hasa linear light image and the processing unit is further configured tocalculate at least one object distance according to a position of thelinear light image in the combined image.
 3. The optical distancemeasurement system as claimed in claim 1, wherein in the first imageregions and the second image regions, a dynamic threshold is used toseparate signal information and noise information for calculating thesignal-to-noise ratio.
 4. The optical distance measurement system asclaimed in claim 1, wherein the processing unit is configured to controlthe image sensor to capture images alternatively with the first exposuretime and the second exposure time.
 5. The optical distance measurementsystem as claimed in claim 1, wherein each of the first image regions isone pixel row, a plurality of pixel rows, one pixel column, a pluralityof pixel columns or a rectangular pixel region of the first image, andeach of the second image regions is one pixel row, a plurality of pixelrows, one pixel column, a plurality of pixel columns or a rectangularpixel region of the second image.
 6. A distance measurement method of anoptical distance measurement system, comprising: projecting, by a singlelight source, an optical line on an object; capturing, by an imagesensor, reflected light from the optical line on the object projected bythe single light source to generate a first image with a first exposuretime; capturing, by the image sensor, reflected light from the opticalline on the object projected by the same single light source to generatea second image with a second exposure time; dividing the first imageinto a plurality of first image regions, each having multiple pixels,and calculating a first signal-to-noise ratio of each of the first imageregions; dividing the second image into a plurality of second imageregions, each having multiple pixels, corresponding to the plurality offirst image regions, and calculating a second signal-to-noise ratio ofeach of the second image regions; comparing the first signal-to-noiseratio of each of the first image regions in the first image with thesecond signal-to-noise ratio of the corresponding second image region inthe second image to determine which of the first image region and thecorresponding second image region has a larger signal-to-noise ratio;and combining the first image region having the first signal-to-noiseratio larger than the corresponding second signal-to-noise ratio withthe second image region having the second image-to-noise ratio largerthan the corresponding first signal-to-noise ratio to form a combinedimage that reserves information of different objects at differentdistances in images captured by the image sensor to improve calculationaccuracy, wherein the combined image has a plurality of image regionseach being either (i) a first image region selected from the pluralityof first image regions or (ii) a corresponding second image regionselected from the plurality of second image regions, so that some imageregions of the plurality of image regions of the combined image areselected from the plurality of first image regions, and remaining imageregions of the plurality of image regions of the combined image areselected from the plurality of second image regions.
 7. The distancemeasurement method as claimed in claim 6, wherein the combined image hasa linear light image and the method further comprises: calculating atleast one object distance according to a position of the linear lightimage in the combined image.
 8. The distance measurement method asclaimed in claim 6, further comprising: determining the firstsignal-to-noise ratio of each of the first image regions according to adynamic threshold; and determining the second signal-to-noise ratio ofeach of the second image regions according to the dynamic threshold. 9.The distance measurement method as claimed in claim 6, wherein each ofthe first image regions is one pixel row, a plurality of pixel rows, onepixel column, a plurality of pixel columns or a rectangular pixel regionof the first image, and each of the second image regions is one pixelrow, a plurality of pixel rows, one pixel column, a plurality of pixelcolumns or a rectangular pixel region of the second image.
 10. Anoptical distance measurement system, comprising: a single light sourceconfigured to project an optical line on an object; an image sensorconfigured to capture reflected light from the optical line on theobject projected by the same single light source to generate a firstimage and a second image respectively with different exposure times andcontaining a linear light image; and a processing unit coupled to theCMOS image sensor, and configured to receive the first image and thesecond image, divide the first image into a plurality of first imageregions, each having multiple pixels, and calculate a signal-to-noise ofeach of the first image regions, divide the second image into aplurality of second image regions, each having multiple pixels,corresponding to the plurality of first image regions and calculate asignal-to-noise of each of the second image regions, compare thesignal-to-noise ratios of the first image regions in the first image andthe corresponding second image regions in the second image to determinewhich of the first image regions and second image regions have a largersignal-to-noise ratio, and combine a part of image regions selected fromthe first image and a part of image regions selected from the secondimage according to signal-to-noise ratios of the image regions to form acombined image that reserves information of different objects atdifferent distances in images captured by the image sensor to improvecalculation accuracy, wherein the combined image has a plurality ofimage regions, each being either (i) a first image region selected fromthe plurality of first image regions or (ii) a corresponding secondimage region selected from the plurality of second image regions, sothat some image regions of the plurality of image regions of thecombined image are selected from the first image, and remaining imageregions of the plurality of image regions of the combined image areselected from the second image.